1. Field of the Invention
The present invention relates to a liquid crystal display device and a fabricating method thereof, and more particularly, to a liquid crystal display device and a fabricating method thereof having a reduced non-display area.
2. Discussion of the Related Art
Generally, a liquid crystal display device controls the light transmittance of liquid crystals in liquid crystal cells that are arranged in a matrix form, such that a picture is displayed in accordance with video signals. A liquid crystal display device includes an active area in which the liquid crystal cells are arranged in a matrix form. Further, a liquid crystal display includes a non-active area having driving circuits for driving the liquid crystal cells in the active area.
FIG. 1 is a plane view illustrating a liquid crystal display device of the related art. FIG. 2 is a cross-sectional view of the liquid crystal display device taken along line II—II of FIG. 1. Referring to FIGS. 1 and 2, the related art liquid crystal display device includes an actual display area 4 having upper and lower substrates bonded to each other with a sealant. Liquid crystal cells (not shown) are positioned between the upper and lower substrates for displaying a picture. Each of the liquid crystal cells contains a plurality of liquid crystal molecules.
More particularly, a sealant 2 is to bond the upper substrate 11 and the lower substrate 1 to each other, as shown in FIG. 1. An upper alignment layer 10 on the upper substrate 11 and a lower alignment layer 12 on the lower substrate 1 determine the initial molecular arrangement of liquid crystal molecules. A non-display area is adjacent to the sealant 2 between the upper substrate 11 and lower substrate 1 within the boundaries of the space between the upper and lower alignment layers 10 and 12.
The actual display area 4 of the liquid crystal display device includes the area of the upper substrate 11 where a black matrix 20, color filters 16, common electrodes 14, and an upper alignment layer 10 are formed thereon, and the lower substrate 1 where thin film transistors 25, 26, 27, 28, and 30, pixel electrodes 22, and a lower alignment layer 12 are formed thereon and facing into the upper substrate 11. As shown in FIG. 2, spacers 24 sustain a gap between the upper substrate 11 and the lower substrate 1. Liquid crystal molecules (not shown) are injected in the space between the upper substrate 11, the lower substrate 1, and the spacers 24.
On the upper substrate 11, the black matrix 20 is formed in a matrix form to divide the surface of the upper substrate 11 into a plurality of cell areas in which the color filters 16 are formed to prevent optical interference between adjacent cells. The three primary colors of red, green, and blue are sequentially formed on the upper substrate 11 as color filters 16. As shown in FIG. 2, each of the color filters 16 of the three primary colors is formed by depositing and patterning a material, absorbing white illumination and transmits only light with a specific wavelength, such as red, green or blue, on the entire surface of the upper substrate 11 where the black matrix 20 is formed. The common electrode 14 is formed of indium tin oxide (ITO), which is a transparent conductive material, on the color filter where the black matrix 20 and the color filters 16 are formed. Subsequently, a polyimide (PI) is printed on the common electrode 14 and rubbed to form the upper alignment layer 10, thereby completing the upper substrate 11.
On the lower substrate 1, the TFT switching the liquid crystal cell includes a gate electrode 25 projected from a gate line (not shown), a source electrode 28 projected from a data line (not shown), and a drain electrode 30 connected to a pixel electrode 22 through a contact hole 23. Further, the TFT includes a gate insulating layer 6 to insulate the gate electrode 25, the source electrode 28, and the drain electrode 30, and semiconductor layers 26 and 27 to form a channel region between the source electrode 28 and the drain electrode 30 as a result of a gate voltage supplied to the gate electrode 25. More particularly, the TFT selectively supplies a data signal from the data line to the pixel electrode 22 in response to a gate signal from the gate line.
The pixel electrode 22 is located in a cell area defined by the data lines and the gate lines and is formed of a transparent conductive material with a high light transmittance. The pixel electrode 22 is formed on a protective layer 8 deposited on the entire surface over the lower substrate 1 and is electrically connected to the drain electrode through the contact hole 23 formed in the protective layer 8. After printing the lower alignment layer 12 over the lower substrate 1 in which the pixel electrode 22 is formed, a rubbing process is carried out to complete the lower substrate 1.
A sealant 2 is formed along the peripheral area of the upper substrate 11 and the lower substrate 1. The sealant 2 is formed by a printing method or a dispensing method. Subsequently, spherical-shaped spacers 24 are dispersed between the substrates. Then, the upper substrate 11 and the lower substrate 1 are positioned to be attached to each other. Liquid crystal molecules are then injected and sealed between the substrates, thereby completing the liquid crystal display device.
FIG. 3 is a plane view illustrating a non-display area of the liquid crystal display device shown in FIG. 1. As shown in FIG. 3, the non-display area E includes an alignment layer area A formed at a specific area from an end portion 36 of the actual display area and a sealant area C where the sealant 2 is formed. Further, a buffer area B is formed between the alignment layer area A and the sealant area C, and an area D is defined between the sealant 2 and an end portion 32 of the upper substrate 11.
To further reduce the size and weight of an LCD panel, it is desirable to reduce the size of the non-display area while maintaining the size of the actual display area. However, the alignment layer area A formed in the non-display area E has to have a specific area from the end portion 36 of the actual display area because of the material characteristic of polyimide as well as because polyimide printing equipment cannot be precisely controlled when printing polyimide. More specifically, the non-display area E has to have the alignment layer area A with a specific gap from the end portion 36 of the valid display area to the end portion 34 of the alignment layer. Further, the buffer area B should be secured because the sealant 2 in the paste state may be dispersed to form the sealant 2, and because a margin of error for the printing equipment used in printing polyimide must be considered.
Although the sealant area C can be reduced in order to reduce the size of the non-display area E, such a reduction reduces the bonding area where the sealant 2 is formed. If the bonding area of the sealant 2 is reduced, the adhesion between the upper and lower substrates 11 and 1 decreases substantially, which may cause the liquid crystals to leak out. Further, if the width of the sealant 2 is reduced due to the reduction of the sealant area C, cell gaps become non-uniform, thereby generating a stain. Due to such problems, there is a limitation in reducing the width of the sealant 2. Thus, a new structure and a method are needed to reduce the non-display area while maintaining the size of the actual display area in the liquid crystal display panel.